Project time!
Some really low brow, low digits T&M action this evening: testing an old analogue panel meter I have. This is being used shortly for a project which I will detail.
![](https://imgur.com/nnfDKip.jpg)
So the project in question has been on the go for the best part of 10 years and materialised in reality about 4 years ago. The ultimate goal is to build a fairly boring sounding voltmeter. This went through several incarnations already.
The first was a simple 2n3819 based differential amplifier which required some nulling and a high supply voltage.
![](https://imgur.com/ieIszBr.jpg)
![](https://imgur.com/f4uEdW8.jpg)
The second was a slightly improved version with an RCA jack for probes. This had an interchangeable RF, AC and DC voltage probe sets (not pictured). The ranges weren't good enough on this one. It did develop a power LED reminding the end user that the battery would melt if you left it on.
![](https://imgur.com/NdxykPC.jpg)
The last one I did used a CMOS opamp and worked off single rail and 9v battery. This had better ranges. But the meter movement was crappy as was my labelling which made it a chore to use. Also the thing didn't have a massive battery in it so kept falling over.
![](https://imgur.com/sg0BqGJ.jpg)
So bring on 2021 and the nice 10/30 ranged 1mA movement turns up. As does a nice black Eddystone box that will fit it.
New incarnation incoming...
Why am I building these crappy things? Well at the end of the day there's something about using something you built to solve problems and create more things that is magical
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/smiley.gif)
Edit: these are still packed away in a box somewhere too
![Popcorn :popcorn:](https://www.eevblog.com/forum/Smileys/default/EatingPopcorn.jpg)
![](https://imgur.com/nyUpsGJ.jpg)